Date: Mon, 5 Feb 2001 10:52:42 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: lauras AT softhome DOT net
cc: djgpp-workers AT delorie DOT com
Subject: Re: stdint.h
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On Sun, 4 Feb 2001 lauras AT softhome DOT net wrote:

> Eli Zaretskii writes:
> > However, I didn't find any evidence that an int is faster than a char.  
> > Can you provide such an evidence, e.g., by looking at the code produced 
> > by gcc 2.9X and counting cycles?
> 
> I tried. I was wrong - the difference between two versions is very little.
> 
> Here is my "benchmark":
> 
> int main(void)
> {
>    unsigned char x, y, z, t, u, v;
>    for (x = 0; x < 200; x++)
>       for (y = 0; y < 200; y++)
>          for (u = 0; u < 200; u++)
>             for (v = 0; v < 200; v++)
>             {
>                z = x * y;
>                t = z - x / y;
>                z = t + u; 
>                t = z - u;
>             }
>    return 0;
> }

This program divides by zero (when y == 0), so its precise timing is
extremely system-dependent (on some systems, it crashes right away).
It also throws away the results of the computations, so a really smart
compiler could transform it into a no-op.

I modified the program as shown below (removing the unsigned qualifier
while I was at it, to let the compiler work with processor's native
data types), and the results on a P166 were:

     int version:   41 seconds
     short version: 45 seconds
     char version:  36 seconds

int main(void)
{
   char x, y, z, t, u, v;
   for (x = 0; x < 100; x++)
      for (y = 1; y < 101; y++)
         for (u = 0; u < 100; u++)
            for (v = 0; v < 100; v++)
            {
               z = x * y;
               t = z - x / y;
               z = t + u; 
               t = z - u;
            }
   return t;
}